Risque de modèle de volatilité

The risk-return trade-off being the very substance of finance, volatility has always been an essential parameter for portfolio management. Moreover, the generalization of the use of derivatives has placed in the forefront the concept of volatility risk: i.e. the model risk generated by treating the volatility as a constant parameter, when it is in fact volatile. Hence the econometrician is asked for accurate measures and reliable forecasts of volatility, not only for pricing and hedging derivatives, but also more generally for portfolio management. The central thesis of this paper is that operational model-free methods of volatility forecasting do not exist any more than do arbitrage opportunities (free lunches) in financial markets. It is for this reason that there exists volatility model risk against which it is illusory to try to immunize. Several specific components of this model risk are analyzed. One will imply that the choice of a volatility model for a given financial application always confronts one with a risk-return trade-off on the model itself. L'arbitrage rendement - risque étant la substance de la finance, la volatilité a toujours été un paramètre essentiel pour la gestion de portefeuille. La généralisation de l'utilisation de produits dérivés a en outre mis sur le devant de la scène le concept de risque de volatilité, c'est-à-dire en quelque sorte le risque de modèle généré par la vision de la volatilité comme un paramètre constant, alors que celle-ci est elle-même volatile. Ainsi, des mesures précises et des prévisions fiables de la volatilité sont demandées à l'économètre, non seulement pour l'évaluation et la couverture des actifs dérivés0501s aussi plus généralement pour la gestion de portefeuille. La thèse centrale de cet article est que des stratégies opérationnelles de prévision statistique de la volatilité qui seraient model-free n'existent pas davantage que les opportunités d'arbitrage ( free lunch ) sur les marchés financiers. D'où le risque de modèle de volatilité contre lequel il est illusoire de vouloir s'immuniser. Plusieurs composantes spécifiques de ce risque de modèle sont analysées. On en déduira que le choix d'un modèle de volatilité pour une application financière donnée confronte toujours à un trade-off rendement/risque sur le modèle lui-même.Volatility, model risk, ARCH, GARCH, forecasting, structural model, Volatilité, risque de modèle, ARCH,GARCH, prévision, modèle structurel

Manufacturing Process Analysis for Simultaneous Synthesis and Deposition of Turbostratic Graphene on Absorbers in Solar Thermal Collector Applications

The absorber section is a critical component in solar thermal collectors and is responsible for converting electromagnetic radiation into sensible thermal energy. The optical properties of the surface of the absorber dictates the effectiveness of this conversion. In this work, a manufacturing process is designed to provide bulk surface treatment for solar absorber plates in order to enhance their radiative properties. The process utilizes a novel approach of graphene synthesis and simultaneous deposition via high pressure blasting of graphite. The results show enhanced spectral, thermal and electrochemical performance of the absorber due to the turbostratic nature of graphene adhesion to its surface, especially when three blasting passes are used. The absorptivity of the absorber exhibited a 7% increase when three passes were applied on its surface. Using graphene has also enhanced the corrosion resistance of the absorber plate. This manufacturing system will provide a facile yet effective treatment of absorbers with various degrees of automation. Applied as a final layer, the process can be retrofitted to existing manufacturing facilities with minimum overhead costs

Manufacturing Process Analysis for Simultaneous Synthesis and Deposition of Turbostratic Graphene on Absorbers in Solar Thermal Collector Applications

The absorber section is a critical component in solar thermal collectors and is responsible for converting electromagnetic radiation into sensible thermal energy. The optical properties of the surface of the absorber dictates the effectiveness of this conversion. In this work, a manufacturing process is designed to provide bulk surface treatment for solar absorber plates in order to enhance their radiative properties. The process utilizes a novel approach of graphene synthesis and simultaneous deposition via high pressure blasting of graphite. The results show enhanced spectral, thermal and electrochemical performance of the absorber due to the turbostratic nature of graphene adhesion to its surface, especially when three blasting passes are used. The absorptivity of the absorber exhibited a 7% increase when three passes were applied on its surface. Using graphene has also enhanced the corrosion resistance of the absorber plate. This manufacturing system will provide a facile yet effective treatment of absorbers with various degrees of automation. Applied as a final layer, the process can be retrofitted to existing manufacturing facilities with minimum overhead costs

Isolation and X-ray crystal structure of tetrahydroisoquinoline alkaloids from Calycotome villosa Subsp. intermedias

Two tetrahydroisoquinoline alkaloids were extracted from the alkaloid fraction of a methanol extract of the seeds of Calycotome Villosa Subsp. intermedia. Their structures were established as (R)-1-hydroxymethyl-7-8-dimethoxy-1,2,3,4-tetrahydro- isoquinoline (1) and (S)-7-hydroxymethyl-2-3-dimethoxy-7,8,9,10-tetrahydroisoquinoline chloride (2) by spectroscopic techniques and X-ray diffraction analysis

Prevalence of sleep disorder in type 2 diabetes Mellitus patients and it's related factors

Background & objectives: There are some evidences for the decrease of sleep quality among diabetic patients. Because of negative impact of blood glucose on sleep disorders, we aimed at investigating The prevalence of sleep disorders in patients with type 2 diabetes and its risk factors. Methods: This cross-sectional study was carried out on 507 patients with type 2 diabetes in Gonabad in 1391. for data collection valid and reliable questionnaire and the Pittsburgh Sleep Quality questionnaire were used.The data were analyzed by software SPSS 20 and descriptive statistics. Results:The prevalence of sleep disorders in this study was 50/7%. 65% of participants were women, and mean age of patients in the two groups with and without sleep disorders were respectively 58/56 and 57/90. Sleep disorder score significantly higher in women than men, and the marital status, occupation, daily glibenclamide, a significant relationship was observed in other diseases and improve sleep. Conclusion: The prevalence of sleep disorders in patients with diabetes is high. Because of known effects of sleep disorders in diabetes, It is suggested to plan a sleep health program in patients with diabetes and it needs more attention

Palladium-Catalyzed Coupling of 3-Halo-Substituted Coumarins, Chromenes, and Quinolones with Various Nitrogen-Containing Nucleophiles

International audienceAn efficient and general palladium‐catalyzed coupling reaction between 3‐bromocoumarins, 3‐bromoquinolin‐2(1H)‐ones, and 3‐iodo‐2H‐chromenes with a variety of nitrogen‐containing nucleophiles (azole, amide, lactam, sulfonamide, aniline, amine, and urea) is described. The reaction proceeded rapidly and cleanly in dioxane providing the coupling products in good to excellent yields. The chemoselectivity of this reaction was also studied with polyhalocoumarins. Under optimized conditions, these underwent a site‐selective amination at the C‐3–Br bond, regardless of the nature of the nitrogen‐containing nucleophile used

Evolution of Fermentation Parameters of Ensiled Sugar Beet Pulp During Storage

This study was carried out to evaluate the silage quality of sugar beet pulp throughout the storage period and so obtain useful information for farmers and livestock feed industry. All silages were prepared in bags of 50 kg in anaerobic conditions. Silages were sampled on months 0, 3 and 6.the results indicate a net decrease of the pH to around 3.8 after 3months silage and remained stable, an important increase of the lactic acid and a slight increase in the acetic acid. But there is a total absence of propionic acid and butyric acid and that after 3 months and 6 months silage. These results have allowed classifying silage 3 months and 6 months between a good and excellent. the results indicated that there is a positive and significant correlation between lactic and acetic acid (r = 0.955 **) and between DM and pH (r = 0 .630**), but there is a negative and significant correlation between pH and lactic acid (r = -0.896**), between DM and lactic acid (r = -0.731**), between acetic acid and pH (r= -0.921**) and between acetic acid and DM (r= -0.678**). Keywords: Sugar beet pulp; silage; VFAs; pH; Storage period

Optimisation des Performances de Rayonnement d'une Nouvelle Structure d'Antenne Patch de Forme Carrée pour un Lecteur RFID

L’objectif principal de ce travail est d’optimiser les performances de rayonnement d’une nouvelle structure d'antenne patch de forme carrée. Cette antenne est excitée par une ligne microruban ayant un port d’alimentation adapté

Prevalence of low back pain and its related factors among pre-hospital emergency personnel in Iran

Objective: Low back pain is one of the most important job injuries among emergency medical personnel. This study was carried out to investigate the prevalence of low back pain as well as its physical, mental and managerial predisposing factors among emergency medical personnel in Iran. Methods: In this analytical cross-sectional study we recruited 298 pre-hospital emergency medical personnel based on census sampling. Data were gathered using Nordic and a research-made questionnaire related to physical, mental and managerial back pain factors. Data were analyzed using SPSS version 20. Descriptive and analytical tests including chi-square test were used appropriately. P value less than 0.05 was considered as the level of significance. Results: Findings showed that 46.3% of pre- hospital emergency technicians had a history of low back pain with different intensities. We observed a significant relationship between age, work experience, occupational-physical factors with low back pain (P > 0.001). However, there was no significant relationship between occupational-managerial factors and mental-occupational factors with low back pain (P > 0.05). Conclusion: Results show that the prevalence of back pain among emergency medical personnel is high. Identifying the factors associated with back pain can help the managers as well as the personnel to control the problem of back pain and increase employees’ productivity

Graphene synthesis techniques and environmental applications

Graphene is fundamentally a two-dimensional material with extraordinary optical, thermal, mechanical, and electrical characteristics. It has a versatile surface chemistry and large surface area. It is a carbon nanomaterial, which comprises sp2 hybridized carbon atoms placed in a hexagonal lattice with one-atom thickness, giving it a two-dimensional structure. A large number of synthesis techniques including epitaxial growth, liquid phase exfoliation, electrochemical exfoliation, mechanical exfoliation, and chemical vapor deposition are used for the synthesis of graphene. Graphene prepared using different techniques can have a number of benefits and deficiencies depending on its application. This study provides a summary of graphene preparation techniques and critically assesses the use of graphene, its derivates, and composites in environmental applications. These applications include the use of graphene as membrane material for the detoxication and purification of water, active material for gas sensing, heavy metal ions detection, and CO2 conversion. Furthermore, a trend analysis of both synthesis techniques and environmental applications of graphene has been performed by extracting and analyzing Scopus data from the past ten years. Finally, conclusions and outlook are provided to address the residual challenges related to the synthesis of the material and its use for environmental applications